Thinkpads Forum

Sometime last week, I left my T420 for a bit, and when I came back, I noticed the computer was off, but the power button light was pulsating. The light was on, but would quickly dim. When pressing the button, nothing would happen. After unplugging the power and removing the battery, the light would then start blinking in 1 second increments.

After doing some research, I ordered a replacement CMOS battery and Keyboard. Before putting in the CMOS battery, I started the T420 and got this message:

“Real Time Clock Error – Check Date and Time Settings
System CMOS Checksum bad

Press Esc to continue and F1 to enter Setup”

After more research, the first suggestion for this message was to replace the CMOS battery, which I did. The new CMOS did nothing. A series of blinks, then pulsating. Replaced the keyboard and nothing. Series of blinks, then pulsating.

I have tried unplugging the CMOS and pressing the power button for 30 seconds to completely drain any power. When I start up, I get the CMOS error above again, I’ve gone into BIOS, reset to system defaults, and when the computer restarts, I get the pulsating light again.

Any idea what I can do to remedy the situation? I’m lost.

As a follow up, I tried RealBlackStuff's last recommendation in this post: viewtopic.php?f=71&t=131050

Again, when I get everything hooked up, I'm getting the pulsating light. I've even taken out/swapped the ram. Same thing. Pulsating light. Even kept the CMOS unplugged and only put in A/C power, pulsating light.

Your help is greatly appreciated.

Had the same problem, and solved it.
(1) Remove battery and AC
(2) Remove CD drive and everything in the USB ports
(3) Remove any additional RAM (leave one stick in)
(4) Remove cmos battery
(5) Hold the power button in for 30 seconds
(6) Leave laptop with no power overnight (this steo is annoying, but important)
(7) Plug in AC and power on --> you'll get a cmos error
(8) Power off, put everything back in, and you should be good to go